A methanol carbonylation process (methanol-acetic acid process) is known as a method for industrially producing acetic acid. In this process, for example, methanol is reacted with carbon monoxide in the presence of a catalyst in a reactor to form acetic acid, the resulting reaction mixture is subjected to evaporation in an evaporator to give a vapor phase, the vapor phase is purified through a light ends column and subsequently through a dehydration column to give an acetic acid product, or further purified through a heavy ends column subsequent to the dehydration column, and, further through a product column to give an acetic acid product.
In the acetic acid production process as above, an offgas from a process typically using a reaction system or a purification system includes useful components (such as methyl iodide, water, methyl acetate, and acetic acid). Before discarding of the offgas, the useful components are recovered from the offgas typically by absorption treatment with an absorbing solvent in a scrubbing system. However, the offgas also includes hydrogen iodide. Hydrogen iodide probably corrodes the interior of equipment and facilities in the acetic acid production process and/or causes environmental issues when released into the atmosphere. Removal of hydrogen iodide from such offgas is therefore also required.
Patent Literature (PTL) 1 discloses an acetic acid production method in which a specific process stream is brought into contact with a first absorbent selected from the group consisting of acetic acid, methanol, and methyl acetate, or further brought into contact with a second absorbent including at least one of methanol and methyl acetate, to thereby remove hydrogen iodide from the process stream.